In vehicles, in particular utility vehicles, with a pneumatic brake system, in particular embodied as an electronic brake system (EBS) or an anti-lock brake system (ABS), for adjusting braking pressures from a control unit (ECU), electronic control valves, for example relay valves or axle modulators, can be actuated, which then pneumatically pass a braking pressure to the brake cylinders of the service brakes of the brake system. Depending on a demanded target vehicle deceleration, the adjustment of a braking pressure is superimposed on the electronically adjusted pneumatic braking pressure depending on the actuation of a braking force controller or brake value generator by means of a brake pedal operation by the driver, so that the driver in the autonomously controlled vehicle can also still complete emergency braking himself and/or can override the electronically controlled braking pressure in an emergency.
It is a disadvantage with previous solutions in known vehicles with pneumatic brake systems that there is no electronically controllable fallback in the event of a failure of the electronic actuation of the control valves. The pneumatic fallback of a conventional brake system only functions if the driver also operates the brake pedal. This is not the case as a rule in the case of an autonomously controlled vehicle, in particular if no driver is sitting in the vehicle or the driver is not paying attention.
DE 197 50 932 A1 discloses a brake controller for a rear axle with a relay valve as a control valve, an electronically controlled proportionality valve and a pneumatic braking force controller. The proportionality valve and the braking force controller are connected via pneumatic control inputs to the relay valve and transfer a defined control pressure to the control input of the relay valve. The relay valve in turn adjusts the higher of the two control pressures in proportion as the braking pressure at the brake cylinders of the service brakes of the rear axle. Furthermore, a brake valve is provided, the setting of which is dependent on the operation of the brake pedal by the driver and which determines the braking pressure to be adjusted by the relay valve. In addition, a brake valve control pressure is transferred pneumatically to the braking force controller by the brake valve and at the same time is transferred electrically by control electronics by means of a control signal to the proportionality valve, which then adjusts a corresponding control pressure at the relay valve, wherein with proper operation the control pressure of the braking force controller is set slightly lower than the control pressure of the electronically controlled proportionality valve. In the event of an electrical failure, as a result a fallback is formed, since if the electronically controlled proportionality valve fails or has a fault, the control pressure determined by the braking force controller is automatically higher and is thus used for braking pressure adjustment by the relay valve.
DE 28 18 813 C3 describes an arrangement for preventing spinning of the wheels. In this case, on activating the arrangement a solenoid valve is opened, which releases the working pressure from a pressure reservoir container, so that it can be adjusted at the solenoid control valves on the rear wheels via a directional valve. The solenoid valve is controlled in this case by a comparison device such that in the event of spinning of the rear wheels while driving off, the rear wheels are braked by the solenoid control valves and as a result the speed of the rear wheels is adjusted to the speed of the front wheels. If a braking process is initiated at the same time, the directional valve is changed over so that braking pressure is only fed from the brake valve to the solenoid control valves and deceleration of the wheels takes place as a result.
DE 10 2014 013 882 discloses a method for detecting unintentional pneumatic activation of a relay valve, wherein the relay valve is provided for operating the service brakes and receives demands both from a brake valve and from a controller or regulator for automatic braking.
U.S. Pat. No. 7,520,572 B2 and EP 1 730 006 B1 reveal a method with which the brake valve in addition to the brake pedal can be actuated by an electronic control unit. Therefore, an electronic brake system is provided, the service brakes of which are controlled by the brake valve and by an additional relay valve. On the one hand, the braking demand to the brake valve can be determined by means of the brake pedal or even independently thereof by means of a brake valve actuator that is disposed between the brake pedal and the brake valve. The brake valve actuator is controlled by the electronic control unit by adjusting a control pressure at the brake valve actuator, which is embodied as a pneumatic valve for example, if there is a control signal for decelerating the vehicle, so that the brake valve is actuated.
U.S. Pat. No. 6,659,244 B2 discloses a possible brake valve actuator for U.S. Pat. No. 7,520,572 B2 or EP 1 730 006 B1, which is disposed between the brake pedal and the brake valve and which is implemented as a pneumatic actuator with a piston. If there is a control pressure from the electronic control unit, the pneumatic actuator keeps the piston rod of the brake valve in the actuated position thereof, independently of the position of the brake pedal, in order for example to be able to provide pre-trip functionality when the vehicle is at a standstill.
EP 1 530 529 B1 discloses a pressure control module for a pneumatic brake system of a vehicle. In this case, it is provided that a relay valve controlling the service brake is actuated by means of a directional valve, wherein the actuation is carried out by an ABS control unit depending on whether slip is occurring. Furthermore, it is provided to use such an arrangement in a traction control system by connecting a further directional valve upstream, which connects the compressed air connection of the directional valve to a pressure reservoir container depending on the existence of slip in the drive, so that the pressure at the service brakes can also be increased via the relay valve.
DE 10 2010 050 578 A1 discloses a brake system in which a braking demand is specified by means of a brake valve or a brake pedal device. This is converted in a control device into an electrical signal and a control valve that adjusts the braking pressure at the service brakes is actuated with the electrical signal. If the electronics fail, in the case of redundancy the control valve is controlled pneumatically by the service brake valve via compressed air lines and furthermore adjusts a braking pressure at the service brakes. In this case, the control valve comprises a plurality of solenoid valves and a relay valve. The solenoid valves can increase, maintain or reduce the braking pressure at the service brakes adjusted by the relay valve depending on the desired function by means of the control pressure by energizing the respective solenoid valve.
DE 10 2013 015 949 A1 describes a brake system for assistance in turns, wherein it is provided to adjust a braking pressure at service brakes of the brake system with an electronically controlled multiway valve, wherein a braking pressure is also adjusted if there is no braking demand from a first brake valve forming the brake value transmitter. In this case, the multiway valve and the first brake valve are switched via a shuttle valve to a relay valve that adjusts the braking pressure at the service brakes. In this case, the shuttle valve only provides the higher of the two pressures from the first brake valve and the shuttle valve to the relay valve, so that the electrical demand on the multiway valve can be overridden by the first brake valve.